Lizz - When I start by opening a new project I select the option to create a custom size. Then I put in the dimensions as 12 x 24. I have a wide screen monitor so it's easy for me to see both pages together but on a smaller monitor you may not like how small they appear, it's up to you how you want to create a two page layout. If you don't want to see both together just create each page one at a time.
Tameka - I believe the best way you should do this is group all of the papers and elements on the left side together and do the same for the right side. You will then have two layers, or two pages. While one of the pages is selected right click and "save selection". Browse to find a folder you want to save the page in and save your file as a jpeg. Do the same thing with the second page, save the file with a different name. You will now have two separate pages that are 12 x 12 and can be put in a book for print. Hope that helps, let me know if you are still confused.